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CVE-2021-21985 CISA KEV — actively exploited Ransomware-linked

VMware vCenter Server Improper Input Validation Vulnerability

n/a — VMware vCenter Server and VMware Cloud Foundation

The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check plug-in which is enabled by default in vCenter Server. A malicious actor with network access to port 443 may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server.

CVSS scoreCritical

9.8

EPSS — exploitation probabilityCritical

100.0%

Vector breakdown

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Published
May 26, 2021
Modified
Aug 12, 2026
Added to KEV
Nov 3, 2021
Federal patch due
Nov 17, 2021

CISA required action

Apply updates per vendor instructions.

Weakness classification

CWE-918Server-Side Request ForgeryCWE-20Improper Input ValidationCWE-470Use of Externally-Controlled Input to Select Classes or Code

Affected packages

unknown packageunknown
GHSA-rg6m-2r9v-c5fj

Proof-of-concept & exploitation references

8 found

Weaponization

Nuclei template

Available

Metasploit module

Not found

Public repositories whose name or description references CVE-2021-21985, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit — cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.

References

How this class of flaw gets exploited

Frequently asked questions

What is CVE-2021-21985?

The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check plug-in which is enabled by default in vCenter Server. A malicious actor with network access to port 443 may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server.

How severe is CVE-2021-21985?

CVE-2021-21985 has a CVSS base score of 9.8 out of 10 (CVSS 3.1).

Is CVE-2021-21985 actively exploited in the wild?

Yes. CVE-2021-21985 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Nov 3, 2021, meaning CISA has confirmed evidence of active exploitation. It is also flagged as used in ransomware campaigns.

What is the EPSS score for CVE-2021-21985?

100.0% - meaning FIRST.org's EPSS model estimates a 100.0% probability this vulnerability will be exploited in the wild within 30 days (100% percentile among all scored CVEs).

Is there exploit tooling available for CVE-2021-21985?

Yes - a public Nuclei template referencing CVE-2021-21985 exist in public repositories we checked. We also found 8 public GitHub repositories referencing this CVE.

What type of vulnerability is CVE-2021-21985?

CVE-2021-21985 is classified under CWE-918, CWE-20, CWE-470 (CWE-918 Server-Side Request Forgery (SSRF)).

Cross-checked against

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